Clonal analysis of the specificity of alloreactive cells: "dominance" of E beta reactive clones.

The present experiments analyze the specificity of cells proliferating in murine mixed lymphocyte cultures (MLC). Lymphocytes from the B10.A(5R) strain, enriched by repeated restimulations with B10.A cells, proliferate specifically in response to B10.BR, B10.A and [B10.A(4R) X B10.A(5R)]F1 stimulators, while showing very limited responsiveness to B10.A(4R) cells. The preferential recognition of determinants on molecules other than Kk or I-Ak was directly proven by isolating 21 T-cell clones, all of which were Ek beta specific. This "dominance" seems to reflect a high frequency of Ek beta reactive T cells in the unselected B10.A(5R) repertoire because: (1) it is already observed in blasts isolated in a primary MLC, (2) it is typical of several independently raised B10.A(5R) anti-B10.A cultures, and (3) it is not found in parallel C57BL/6 anti-B10.BR MLCs that show dominant I-A specificity. Results showing the importance of determinant concentrations expressed by stimulator cells suggest that uncloned T-cell lines are heterogeneous in their "affinities" and that our cloning conditions select cells with high "functional affinity".